Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$103.53	6.326%	$110.0793	$110.08	$110.10	$110.10
Purchase #2	$205.34	8.555%	$222.9068	$222.91	$222.90	$222.90
Purchase #3	$29.86	5.260%	$31.4306	$31.43	$31.45	$31.40
Purchase #4	$75.40	9.496%	$82.56	$82.56	$82.55	$82.60
Purchase #5	$248.98	10.633%	$275.454	$275.45	$275.45	$275.50
Purchase #6	$176.59	13.476%	$200.3873	$200.39	$200.40	$200.40
Purchase #7	$38.33	4.715%	$40.1373	$40.14	$40.15	$40.10
7 purchase totals =	$878.03		$962.9553	$962.96	$963.00	$963.00